#include <cstdio>
#include <deque>
using namespace std;

int main() {
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);
	deque<int> d;
	int n, k;
	scanf("%d %d", &n, &k);
	int a[n+1];
	long long ans =0;
	for(int i=1;i<=n;i++)
		scanf("%d ", &a[i]);
	for(int i=1;i<=k;i++) {
		while(!d.empty() && a[i]<a[d.back()])
			d.pop_back();
		d.push_back(i);
	}
	ans += a[d.front()];
	for(int i=k+1;i<=n;i++) {
		if(d.front() == i-k)
			d.pop_front();
		while(!d.empty() && a[i]< a[d.back()])
			d.pop_back();
		d.push_back(i);
		ans += a[d.front()];
	}
	cout << ans << '\n';
	return 0;
}